Locking fasteners have long been available in which coacting wedge ramps operate to generate wedging forces as the associated nut attempts to back off of the associated bolt and these wedging forces are arranged to urge the nut into tighter engagement with the associated bolt and workpiece. Whereas locking fasteners operating on the wedge ramp principles work very well in static demonstrations they have not achieved any wide-spread commercial acceptance since the nuts associated with the fasteners have tended to back off under the high frequency vibratory loading typically encountered in real life commercial environments.
Recent research has shown that the loosening of nuts is mainly caused by the wind-up or twist that remains in the bolt shank after tightening due to the opposing frictional torques caused by the friction in the threads opposed by the friction between the bolt head and its seat. This wind-up force is large and is constantly acting in a direction to back off the nut. For a bolt and nut tightened in the usual manner it is always present and roughly proportional to the tension load or holding force present in the bolt. It is this basic unwinding force or torque that is the major cause of the vibration loosening of threaded joints.